Biomimetic tissue-engineered articular cartilage repair Articular cartilage injuries cannot self-repair and if left unattended, will lead to osteoarthritis (OA) of the affected joints. A number of different procedures have been developed to repair damaged cartilage, yet a therapeutic strategy that results in a functional and durable cartilage repair has not been achieved. For most tissue engineering repair of osteochondral defects, a single-phase material that is usually deformable and mechanically and structurally uniform has been tested, again without uniform success. One of the major causes for failure of cartilage repair is non-integration between the repair tissue and the surrounding cartilage. Finite element computer modeling indicates that excessive deformation of the repair tissue causes considerable stress at the implant-host interface, which contributes to the failure of the repair tissue. Articular cartilage is a structurally complex tissue, whose function partly depends on the support of intact subchondral bone. We hypothesize that a biphasic composite gran system, one that provides the functional mechanical support at the base of the osteochondral defect and the other that facilitates the repair of articular cartilage, is essential for successful cartilage repair. This biphasic composite graft mimics the physiological structure of the osteochondral interface and provides a favorable mechanical environment that reduces the stress level at the implant- host interface, favoring host-repair tissue integration and facilitating functional repair. DBM has mechanical integrity and contains a variety of intrinsic growth factors that are, at least, 20 times greater in volume concentration than in serum. These growth factors are able to enhance bone healing and modulate the osteochondrogenesis of progenitor cells and may contribute to the constant remodeling of bone tissue through osteoclastic and osteoblastic activities. DBM functions as a reservoir of naturally balanced multiple bioactive factors when it is used to repair bone or cartilage defects. Cartilage tissue can be engineered in vitro with either bone marrow-derived Mesenchymal Stem Cells (MSCs) or culture-expanded chondrocytes in a gelatin sponge or hyaluronan (HA) carrier matrix. Special attention is provided to the optimization of the integration of neo- tissue with that of the host by using HA-oligomers to facilitate such integration In this proposal, a novel dual-phase composite graft composed of DBM and in vitro tissue engineered precartilage (MSCs or chondrocytes) will be tested to repair an osteochondral defect. The objective is to re-evaluate the use of this mechanical factor with a suitable collagenous delivery vehicle for the cell-based therapy of osteochondral defects. This objective will be addressed by the following Specific Aims: SPECIFIC AIM 1. To optimize the conditions for in vitro engineering of cartilage tissue with MSCs or chondrocytes combined into the gelatin or HA matrix. The goal is to prepare an implantable cartilage tissue for resurfacing of the cartilage defect. SPECIFIC AIM 2. To test a biphasic composite graft in a rabbit model and assess the mechanism and sequential events during the repair of osteochondral defects. SPECIFIC AIM 3. To translate these small animal results from Specific Aims 1 and 2 to a larger, clinically relevant animal model (goats) to develop a therapeutic strategy for repair of cartilage defects.